The mechanical properties of thermosetting resins strongly depend on the curing process itself and, hence, it is important to understand the effects of temperature distributions and degree of cure on the mechanical behavior of polymeric matrix composites. Moreover, the understanding of rheological changes during the curing process is essential for the manufacturing process optimization . In this paper, the chemo-rheological behavior of AS/3501-6 graphite/epoxy during the cure process is presented. Dynamic mechanical analyses are employed to determine complex dynamic moduli of composites during the curing process. These experimental results reveal the strong material property dependence on temperature, frequency (time) and degree of cure.
Dynamic transient responses of plates with viscoelastic free damping layers are studied in order to evaluate free layer damping treatment performances. The effects of forcing frequencies and temperatures on free-layer viscoelastic damping treatment of plates are investigated analytically. Young’s modulus ratio of structures to viscoelastic damping materials and the damping layer thickness effects on the damping ability are also explored.
Test efficiency of packaged electronics strongly depends on test time and test cost because test time increase causes the increase of test cost. In this paper, with RF WLP devices fabricated by wafer level package processes, we have demonstrated RF multi-DUT testing technology with superior measurement stability and enhanced package yield in RF wafer level test. We could know that RF multi-DUT testing technology for RF WLP devices in wafer level testing has test time reduction of 61.9% compared to test time of RF single-DUT testing through analyzing test time. This technology can offer a number of significant advantages such as productivity improvement and superior capabilities for high performance RF wafer level testing. RF multi-DUT testing technology is essential in addressing future needs for testing RF WLP devices on the wafer.
The wet-end dynamics of a paper mill was analyzed to characterize its dynamic behavior during the grade change of paper. The model representing the wet-end section is developed based on the mass balance relationships written for the simplified wet-end white water network. From the linearization of dynamic model, higher-order Laplace transfer functions were obtained followed by the reduction procedure to give simple lower-order models in the form of 1??-order or 2??-order plus dead times. The dynamic response of the wet-end is influenced both by the white water volume and by the level of wire retention. Effects of key manipulated variables such as the thick stock flow rate, the ash flow rate and the retention aid flow rate on the major controlled variables were analyzed by numerical simulations. The simple dynamic model developed in the present study can be effectively used in the operation and control of paper mills.
Transition metal hydroxides (M-OH) and their heterostructures (X|M-OH, where X can be a metal, metal oxide, metal chalcogenide, metal phosphide, etc.) have recently emerged as highly active electrocatalysts for hydrogen evolution reaction (HER) of alkaline water electrolysis. Lattice hydroxide anions in metal hydroxides are primarily responsible for observing such an enhanced HER activity in alkali that facilitate water dissociation and assist the first step, the hydrogen adsorption. Unfortunately, their poor electronic conductivity had been an issue of concern that significantly lowered its activity. Interesting advancements were made when heterostructured hydroxide materials with a metallic and or a semiconducting phase were found to overcome this pitfall. However, in the midst of recently evolving metal chalcogenide and phosphide based HER catalysts, significant developments made in the field of metal hydroxides and their heterostructures catalysed alkaline HER and their superiority have unfortunately been given negligible attention. This review, unlike others, begins with the question of why alkaline HER is difficult and will take the reader through evaluation perspectives, trends in metals hydroxides and their heterostructures catalysed HER, an understanding of how alkaline HER works on different interfaces, what must be the research directions of this field in near future, and eventually summarizes why metal hydroxides and their heterostructures are inevitable for energy-efficient alkaline HER.
Abstract Three practically important reliability-related questions for solder joint interconnections (SJIs) in automotive electronics, and particularly in its actuator and sensor electron devices, are addressed in this analysis:Could inelastic strains in the solder material be avoided by a rational physical design of the IC package, and, if not, could the sizes of the peripheral inelastic strain areas be predicted and minimized? It is clear that the low cycle fatigue lifetime is inversely proportional to the sizes of the inelastic zones and that the material's fatigue lifetime could be improved dramatically, if the induced strains remain within the elastic range. The Palmgren-Miner rule of linear accumulation of damages can be used, instead of Coffin-Manson relationships, in such a situation.Realizing that, because of the inevitable uncertainties, the difference between highly reliable and an insufficiently robust electronic products is “merely” in the levels of their never-zero probabilities of failure, could these probabilities be assessed, and could this be done at the design stage? A possibility of doing that is particularly critical for SJIs, the most vulnerable structural elements in the today's IC package designs. Reliability of an electronic material or a product cannot be assured, if it is not quantified, and, because of the inevitable and critical uncertainties, this should be done on the probabilistic basis.Should SJI accelerated testing based on costly, time- and labor-consuming and, because of temperature dependency of material properties, possibly even misleading temperature cycling, be replaced by a more physically meaningful, less expensive and more trustworthy accelerated test vehicle, and could low-temperature/random-vibrations bias be employed in this capacity? The rationale behind such a question has to do with the facts that the highest thermal stresses take place at the lowest temperature conditions, and that fatigue cracks, whether elastic or inelastic, propagate most rapidly, when the material experiences random vibrations. This technique has been already reduced to practice in an industrial lab two years ago. The objective of the analysis is to shed light, by using analytical (“mathematical”) modeling, rather than widely spread computer simulation, on the mechanical behavior and the underlying physics of failure in the SJI. Future work should focus primarily on experimentations to confirm theoretical findings and recommendations.
There is currently much interest in thin-film layered systems and considerable attention has been given Fe/Cr(001) systems were quantitatively investigated in this study. Cr adatoms on the Fe(001) surface and Fe adatoms on the Cr(001) surface favored hollow sites as their adsorption site. The adsorption energies were 4.25 and 3.22 eV for each system and the surface diffusion energy barriers were calculated to be 0.99 eV for Cr/Fe(001) and 1.74 eV for Fe/Cr(001). Cr adatoms showed a strong antiferromagnetic phase on the Fe substrate with their spins aligned in the opposite direction to the magnetic moment of the Fe substrate, while the magnetization of ferromagnetic Fe atoms was weakened with adsorption onto the Cr substrate. During the surface diffusion process, energy states of 3d electrons in the adatom shifted toward higher levels, which corresponds to overcoming the energy barrier in both systems.
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